How to create squared glow?
That image was created with a bunch of overlapping transparent planes which were created by extruding parts of a circle:

Add a circle (Shift+A&gt; Mesh &gt; Circle. Note that you may want to increase the Vertices in the redo menu for a smother curve.) Then delete some of the vertices so you only have part of a circle:


Extrude (E) and cancel the transform to leave the extruded vertices where they are (Esc). Then scale along the normals with AltS so you have this shape:


Repeat steps 1 and 2 varying the amount of vertices you delete from the circle until you have several different sizes. Then duplicate (ShiftD) rotate (R) them around (make sure you move them slightly on the Z axis to avoid Z-fighting) so you have something like this:


Duplicate and rotate the entire bunch a couple times for good measure (again moving on the Z-axis) and add a couple circles for effect:


Add a material for additive blending (see How to get additive blending in cycles?):


Insert a rotation keyframe for all of them (press I&gt; Rotation to insert a keyframe on the selected objects), then go to a later frame and run Randomize Transform (Space&gt; Search &gt; Randomize Transform). In the Redo menu at the bottom of the Tool shelf (N in the 3D view), Enable Randomize Rotation and set the Z to 180. Then insert another Rotation keyframe.


Result:
animated gif http://www.pasteall.org/pic/show.php?id=65211
blendfile